Lumbar puncture (LP) is an attractive route for delivering novel therapies to the nervous system because it is safe in patients; performed at the bedside; and FDA-approved for conventional drugs. However, its use for gene delivery has to date been ineffective; has not met safety principles; and has failed to target neurons. We have developed highly effective gene transfer to the primary sensory neurons of the dorsal root ganglia (DRGs) via LP, i.e. intrathecally (IT), using self-complementary recombinant adeno-associated virus serotype 8 (sc-rAAV8). A single administration of sc-rAAV8 expressing the analgesic gene prepro--endorphin (ppEP) or a mutant form of the rat anti- inflammatory gene interleukin-10 (rIL10/F129S) led to highly significant (p<0.0001) relief of symptoms for e3 months in a rat chronic neuropathic pain model, an important functional outcome. The hypothesis of this application is that sc-rAAV8 via LP is a viable gene delivery product for intractable chronic pain usable by clinicians outside of specialized research centers. In order to investigate/establish the potential for clinical translation, we propose the following Specific Aims: Aim 1. To quantify DRG transduction by stereology in the closed vs. open IT space, characterize serological immunity to the IT vector, and determine organ distribution. Aim 2. To identify the strongest candidate therapeutic gene in the neuropathic pain model and to define if there is pharmacological synergy with conventional pain treatments. Aim 3. To test the antinociceptive efficacy of the approach in a new rat model reflecting pain in patients with incurable cancer, a possible future clinical trial-scenario. Aim 4. To test if IT sc-rAAV8 effectively transduces DRG neurons in large animals. Significance & future perspective: Chronic pain affects 50 million Americans and incurs costs of >$100 billion/year in the US alone (as stated in PA-07-282). This application proposes a gene therapy approach, which, if the Research Plan succeeds, will become a candidate for clinical development in patients with severe pain from advanced malignancies. IT sc-rAAV8 may serve as a tool for proof-of-mechanism trials, e.g. to validate microglial activation as therapeutic target in humans, and may also become a new drug for otherwise intractable chronic pain.